There's nothing stopping developers from doing server-side validation before sending markup to clients. It seems like the majority of developers have never rea

There's nothing stopping developers from doing server-side validation before sending markup to clients. It seems like the majority of developers have never really wanted to make that cost-benefit tradeoff, though. I ran tons of websites declaring an xhtml doctype through https://validator.w3.org/ https://validator.w3.org/ back before HTML5 when xhtml was still trendy: almost all of the "xhtml" websites failed validation.